This invention relates to a wire cut electric discharge machine in which the tension and the fusing current of a wire electrode are automatically controlled to cut the latter by fusing.
FIG. 1 is an explanatory diagram showing one example of a wire electrode cutting section in a conventional wire cut discharge machine. In FIG. 1, reference numeral 1 designates a wire electrode; 2, a workpiece to be machined with the wire electrode 1; 3, a cutter blade for cutting the wire electrode 1; 4, an air cylinder coupled to the cutter blade 3; 5 and 6, air pressure sources connected to the air cylinder 4 to move the cutter blade 3 back and forth; 7, a cuter blade receiving member used in cutting the wire electrode 1; 8, a power source for inducing pulse discharges between the workpiece 2 and the wire electrode 1; 9, a machining start hole formed in the workpiece 2; and 10, an electric feeder die.
The operation of the wire cut electric discharge machine will be described. After the workpiece has been machined, the wire electrode 1 is cut with the cutter blade 3, to remove the used part thereof. In this case, the air pressure source 5 is used to apply an air pressure to the cylinder 4 to move the cutter blade 3 toward the wire electrode 1, so that the cutting of the wire electrode 1 is carried out between the cuter blade 3 and the cutter blade receiving member 7. In this operation, depending on the diameter and kind of the wire electrode 1, the angle of the cutter blade 3 to the wire electrode 1 and the force of pushing it against the latter 1 are changed so that the section of the wire electrode thus cut be as circular as possible. Thereafter, the air pressure source 6 is activated to move the cutter blade 3 away from the wire electrode. The wire electrode 1 thus cut is inserted into a machining start hole 9 in another workpiece 2 and then into the electric feed die 10. Under this condition, discharge energy is supplied through a wire supplying path from the power source 8, to machine the workpiece 1.
As was described above, in the case of the conventional wire cut electric discharge machine, in order to insert the wire electrode into the electric feeder die with ease, the wire electrode cut in the above-described manner must be substantially circular in section, and in order to meet this requirement, it is necessary to mechanically adjust the angle of the cutter blade to the wire electrode and the force of pushing it against the latter depending on the diameter and the kind of the wire electrode. This mechanical adjustment is considerably troublesome. And often the wire electrode thus cut is not circular in section. In this case, it may be difficult to insert the wire electrode into the hole of the electric feeder die.
In order to overcome the above-described difficulties a method of fusing a wire electrode has been proposed in the art, for instance, by Examined Japanese Patent application Publication No. 26455/1986. In the method, current is applied to a wire electrode while a force of tension is being applied to it in the axial direction, so that the wire electrode is heated and elongated. As a result, the wire electrode partially becomes smaller in diameter. Under this condition, the application of the tensile strength is suspended, to allow the current to fuse the part of the wire electrode which has been made smaller in diameter, to cut the latter into two parts. The desired one of the two parts is fed to the wire guide and passed through a desired through-hole formed in the workpiece, and the wire electrode is set as required.
As was described above, the conventional method has a variety of advantages; however, it is still disadvantageous in the following points: First, the construction is considerably intricate. The current for heating a wire electrode and the current for fusing it according to the diameter and the kind of the wire electrode must be controlled using variable resistors. In the control operation, after the wire electrode has been heated with the current, the switch provided for the heating current is opened, and then the switch provided for the fusing current is closed. Thus, the control operation is considerably troublesome.